Age

Menstruum not only flows down the vagina but can also reflux along the fallopian tubes and into the pelvis. It is this refluxed menstruum that is thought to be the cause of endometriosis, though the mechanism remains unknown. However, there are various suggested theories (Thomas and Rock, 1997):

Implantation

Minute fragments of endometrium pass along the fallopian tubes during menstruation and spill into the pelvic part of the peritoneal cavity; this becomes implanted on another pelvic structure such as the ovary, and develops into endometriosis. While shed endometrium is generally necrotic, living fragments have also been found.